1. Field of the Invention
The present invention generally relates to tape guide apparatus and, more particularly, is directed to a ultrasonic tape guide apparatus for use with a video tape recorder or the like, for example.
2. Description of the Prior Art
Roughly classified, rotary type and stationary type tape guide apparatus are known as tape guide apparatus for use in video tape recorders or the like.
The rotary type tape guide apparatus has a feature such that, when a tape is transported, the rotary type tape guide apparatus has a little resistance against the transport of the tape. However, the rotary type tape guide apparatus cannot avoid disadvantages such that the tape is not transported regularly when a bearing used therein is not rotated regularly and that the tape is affected by a force applied thereto from a roller in the width direction, when the tape transport direction is not perpendicular to the rotating direction of the rotating roller. Particularly in the latter disadvantage, if the tape is moved in the width direction, then the tape edge is frequently damaged. For this reason, in case the rotary type tape guide apparatus is employed, assembly parts must be produced at very high accuracy and also the parts must be assembled at very high accuracy, which unavoidably brings various difficulties in the manufacturing process of the rotary type tape guide apparatus.
Although the stationary type tape guide apparatus can assure the stable transport of the tape, it has a disadvantage such that the tape must be transported with a large resistance.
For this reason, it is desired that a tape guide apparatus is of the stationary type which enables a tape to run with a little resistance. An air tape guide is proposed as an example of the desired tape guide apparatus. According to this air type of tape guide apparatus, air is blown from small apertures bored through the surface of the guide member to float the tape so that the tape is transported with a reduced resistance. However, even this air type of tape guide apparatus has new problems, such as when a compressor is needed as an air supply source or the like.
In order to remove the aforesaid shortcomings and to solve the aforesaid problem, the assignee of the present application has previously proposed a ultrasonic tape guide apparatus which makes effective use of ultrasonic waves as described in Japanese Patent Application No. 2-103627. This ultrasonic tape guide apparatus can reduce a resistance against the tape while the advantage such as the stable tape transport provided by the stationary type tape guide apparatus can be maintained.
FIG. 1 is a cross-sectional view illustrative of such prior-art ultrasonic tape guide apparatus that is generally represented by reference numeral 1 in FIG. 1.
In the tape guide apparatus 1, as shown in FIG. 1, a main shaft 5 is implanted on a base 18, and a guide member 2 having a ultrasonic vibrator 3 secured thereto is supported by a cylindrical supporting shaft 7 having a supporting protrusion 7b. Lower and upper flanges 9 and 10 are disposed so as to come in contact with lower and upper end portions of the supporting shaft 7, thereby guiding the edge portion of a tape wrapped around a guide member 2.
The main shaft 5 is constructed so as to be inserted into the lower and upper flanges 9 and 10 and the supporting shaft 7. A height adjusting screw 6 is engaged with the inner circumferential part of the upper end portion of the supporting shaft 7 and is also engaged with a screw 23 formed on the upper end portion of the main shaft 5. Thus, the main shaft 5, the supporting shaft 7, the height adjusting screw 6, the screw 23 and the guide member 2 constitute a supporting member 4.
The upper flange 10 is secured to the upper portion of a mount member 8 by a mount screw 15 and the lower flange 9 is secured to the lower portion of the mount member 8 by fixing pins 22 and 24. The mount member 8 has an element housing portion 8a which is an opening of a rectangular solid configuration having side walls 8b, 8b on the respective sides thereof, as shown in FIG. 2. Stopper engaging apertures 8c, 8c are formed on the two side walls 8b, 8b, respectively.
Each of the stopper engaging apertures 8c is engaged with an engaging protrusion 39a of a disk-shaped stopper 39 made of a rubber. The ultrasonic vibrator 3 is sandwiched by the stoppers 39, thereby hindering the rotation of the guide member 2.
The mount member 8 keeps the lower and upper flanges 9 and 10 in parallel to each other such that the distance between the upper and lower flanges 9 and 10 becomes larger than the length of the guide member 2 by about 0.1 mm.
Referring back to FIG. 1, the lower flange 9 is pushed upwardly by a spring-biasing force of a coil spring 35 disposed in the outer circumference of the main shaft 5 between the lower flange 9 and the base 18. The base 18 has a pin insertion aperture 20 into which is inserted the fixed pin 22 implanted on the lower surface of the lower flange 9.
According to the above-mentioned arrangement, when the height adjusting screw 6 is rotated, then the height of the guide member 2 can be adjusted by a spring-biasing force of the coil spring 35 and against the spring-biasing force of the coil spring 35.
FIG. 3 is a graph graphing the vibrated state of a standing wave generated in the guide member 2 by the application of AC voltage to the ultrasonic vibrator 3 under the condition such that the vibrated state is expanded taken along the line X--X. As shown in FIG. 3, a dashed line N--N represents a node portion of the vibration and the vibration is zero on this line N--N. Assuming that n represents a distance from the end face of the guide member 2 to the node position, then the position of the supporting protrusion 7b in the axial direction is determined as n from the end face of the guide member 2 as shown in FIG. 1.
As clear from the above description, according to the example of the prior art, the mounting member 8 must be produced at high accuracy in order to keep the lower and upper flanges 9 and 10 in parallel and also in order to keep the spacing between the lower and upper flanges 9 and 10 larger than the length of the guide member 2 by about 0.1 mm. Further, as shown in FIG. 2, the lower and upper flanges 9 and 10 are not circular, which makes the manufacturing process of the lower and upper flanges 9 and 10 very difficult. Accordingly, the tape guide apparatus cannot be made compact in size and also cannot be made inexpensive.